From Dr. Eleanor's Book of Common Ants
A.K.A.: Winnow ants
Size: 0.15 in
Where it lives: Winnow ants prefer to nest in rotting wood, but will nest anywhere from soil in open areas to human garbage.
What it eats: The tasty outer coating of seeds and other insects like termites. Winnow ants also like sugary foods.
What’s the big deal?
Aphaenogaster rudis sounds more like an unsavory medical condition than one of the coolest ant species in North America. It doesn’t roll off the tongue like “sugar ant,” “carpenter ant,” “pavement ant” or “fire ant.” So, for the purposes of familiarizing you with one of the best residents on your block, we’ll give Aphaenogaster rudis a nickname: the winnow ant.
Winnow ants are among the most elegant-looking ants around the forest and in your back yard. With their long legs and slender reddish-brown bodies, they pick their paths delicately across the ground like rusty ballerinas. Each medium-to-large worker measuring at about 0.15 inches long can just cover the date on a quarter (MacGown 2008). Although they prefer to nest in decomposing stumps and logs, winnow ants can make the best out of any situation, building their homes in open soil, beneath rocks, and even in human garbage (Enzmann 1947). With one queen and up to 2000 workers, a winnow colony could easily pack a stadium for an ant rock concert (Morales and Heithaus 1998).
Beyond their refined appearance and wide-ranging nesting habits, winnow ants have two qualities that set them apart from the rest of the ants: the helping hand they give forest plants and their ability to use tools.
First, let me tell you about their agricultural talents, and the reason we call them winnow ants. Winnow ants have a special relationship with forest plants. We all know that many plants make seeds. Some plants produce seeds with a special coating called an eliaosome that’s a lot like the hard candy coating on the outside of an M&M. Like the tasty candy shell, the eliaosome coat has a special blend of flavors that is irresistible to winnow ants.
As they pick across the forest floor in search of food, winnow ants often stumble across these seeds. When winnow ants get a whiff of that eliaosome, they can’t help themselves: They have to pick up the seed and carry it back to their nests (Heithaus et al. 2005). Once in the nest, winnow ants feed the outer coating of the seed to their young (Bono and Heithaus 2002).
Unlike most of us, who prefer the chocolaty center of M&Ms, winnow ants eat only the elaisome and leave the seed inside alone. When wheat farmers shuck wheat seeds from their husks, it’s called winnowing. Likewise, winnow ants remove husks from forest seeds. After the seed has been shucked of its eliaosome, the ants don’t need it anymore, so they take it back out of their nest and deposit it on the forest floor. There, the seed, no worse for the wear, is free to sprout and grow into a happy forest herb. Having their eliasome nibbled away by hungry ant babies does not hurt the seeds; in fact, it helps them. When ants pick up these seeds, they protect them from animals that eat the whole seed, and winnow ants plant seeds far away from the seeds’ parents (Canner et al. 2012). This way, the newly planted seeds don’t crowd their parents as they grow.
Seed planting is a successful business for winnow ants and the seeds they plant. Almost two thirds of all herb seeds produced in the forest are picked up by winnow ants (Ness et al. 2009). These are herbs like wild ginger and trillium. Also, when winnow ants are removed from forests, some wildflower abundance drops by 50% (Rodriguez-Cabal 2012). Seed planting also helps the ants. When winnow ants eat that candy coating eliasome, they get all the nutrients they need to make more babies (Bono and Heithaus 2002).
Farming isn’t the winnow ant’s only talent. Like other animals, from woodpecker finches to chimpanzees to humans, winnow ants use tools to gather food. When a winnow ant happens upon liquids too goopy to carry back to her nest, she goes out in the forest and collects bits of leaves and sticks. She takes these bits back to the newfound food and drops them right on top of it (Fellers 1976). These leaves and sticks become little plates for winnow ants. Workers bring the plates back to the nest for the colony to feast from like Sunday churchgoers at a potluck dinner (Banschbach et al. 2006).
Aphaenogaster rudis is a fancy name, but the winnow ant earned it. How many of us have stood in the living city of a forest, awed by the architecture surrounding us? Somewhere, tucked into the hustle and bustle of creatures keeping the forest alive, creep winnow ants, rusty little architects helping shape everything we see on the ground floor.